Interacting selectively and non-covalently with one or more specific sites on an ion channel, a protein complex that spans a membrane and forms a water-filled channel across the phospholipid bilayer allowing selective ion transport down its electrochemical gradient.

AIMS: Protein-protein interactions are critical for the normal membrane trafficking, localization, and function of voltage-gated ion channels. In human heart, the Shaker-related voltage-gated K(+) channel KCNA5 alpha-subunit forms the major basis of an atrial-specific, ultra-rapid delayed rectifier K(+) current, I(Kur). We sought to identify proteins that interact with KCNA5 in human atrium and investigate their role in the I(Kur) complex. METHODS AND RESULTS: Using a glutathione-S-transferase (GST)-KCNA5 C-terminal fusion protein and mass spectrometry-based methods, the scaffolding protein four and a half LIM (for Lin-11, Isl-1, and Mec3) protein 1 (FHL1) was identified as a potential protein partner for KCNA5. Immunoprecipitation experiments confirmed a physical interaction of FHL1 with the K(+) channel complex in human atrium, as well as in Chinese hamster ovary (CHO) cells transfected with both KCNA5 and FHL1. In cotransfected cells, confocal microscopy demonstrated areas of colocalization after immunolabelling both proteins. To investigate the functional effects of this interaction, K(+) currents were recorded in CHO cells transfected with KCNA5 in the absence and presence of FHL1 coexpression. With coexpression of FHL1, K(+) current density was markedly increased, compared with cells expressing KCNA5 alone. This effect was associated with a shift in the voltage dependence of K(+) channel activation to more positive potentials, consistent with findings of I(Kur) in atrial myocytes. FHL1 also increased the extent and speed of K(+) current slow inactivation, with additional effects on the voltage dependence and recovery of this process. CONCLUSION: These results support a role of FHL1 as a key molecular component in the I(Kur) complex in human atrium, where it likely regulates functional expression of KCNA5.

Four-and-a-half LIM domain protein 1B (FHL1B) is an alternatively-spliced isoform of FHL1. In this study, FHL1B was demonstrated to interact with the β catalytic subunit (Cβ) of a type 2A protein phosphatase (PP2A) by yeast two-hybrid screening. Domain studies using a small-scale yeast two-hybrid interaction assay revealed the mediation of protein-protein interaction by FHL1B's C-terminus. Interaction between FHL1B and PP2A was further verified by co-immunoprecipitation. FHL1B was also shown to shuttle between nucleus and cytoplasm at different phases of the cell cycle. These data suggest that the FHL1B/PP2A(Cβ) interaction may illustrate a novel cell-cycle regulatory pathway.

Four and a half LIM domains 1 (FHL1) belongs to a family of LIM-only proteins that regulate gene transcription, cell proliferation, differentiation and apoptosis. However, the biological function of FHL1 remains largely unknown. We used a yeast two-hybrid system and identified receptor interacting protein of 140kDa (RIP140) as a novel FHL1-binding protein. RIP140 interacted with FHL1 both in vitro and in mammalian cells and estrogen enhanced this interaction. All domains of FHL1 are required to interact with RIP140. Overexpression of FHL1 enhanced RIP140 repression of estrogen signaling in breast cancer cells in a reporter assay, whereas reduction of endogenous FHL1 with FHL1 small interfering RNA abolished this effect. Furthermore, overexpression of the FHL1 deletion mutant that lacks the RIP140-binding sites had no effect on RIP140 repression of estrogen signaling. Consistent with the results of the reporter assays, FHL1 and RIP140 synergistically inhibited the transcription of the estrogen-responsive gene pS2. The results presented here suggested the cooperative transcriptional regulation of estrogen signaling by FHL1 and RIP140, and might provide a new regulation mechanism by which estrogen signaling-related diseases such as breast cancer develop.

The process in which relatively unspecialized cells, e.g. embryonic or regenerative cells, acquire specialized structural and/or functional features that characterize the cells, tissues, or organs of the mature organism or some other relatively stable phase of the organism's life history. Differentiation includes the processes involved in commitment of a cell to a specific fate and its subsequent development to the mature state.

The process whose specific outcome is the progression of the muscle over time, from its formation to the mature structure. The muscle is an organ consisting of a tissue made up of various elongated cells that are specialized to contract and thus to produce movement and mechanical work.

Using a cDNA clone derived from a human muscle library we have identified a novel and highly conserved 2.3kb homologue which is highly expressed in skeletal muscle. The partial sequence contains at least three LIM domains and shows greatest homology with the group of LIM-proteins associated with the cytoskeleton and focal adhesion plaques which include zyxin and paxillin. This homologue is maximally expressed in differentiated ovine primary muscle cultures. It is also expressed in the ovine fetus from at least 50 days of gestation and is increasingly upregulated from 120 days of gestation to 8 weeks after birth after which it declines. This period corresponds to the period of greatest muscle fibre hypertrophy and suggests a role for this homologue in either the elaboration of muscle fibre matrix anchorage or the regulation of muscle fibre hypertrophy itself.

Four and a half LIM protein 1 (FHL1) has been linked to carcinogenesis. However, the role of FHL1 in lung cancer remains unclear and the detailed mechanism underlying its tumor suppressive role is poorly understood. The purpose of this study was to examine FHL1 expression in lung cancer patients and to investigate how it was associated with lung cancer cell growth. Immunoblotting and immunohistochemistry showed that FHL1 protein was downregulated in over 90% of 80 lung cancer patients. FHL1 expression was strongly correlated with tumor histological types (P<10(-4) ) and the differentiation of the tumor (P=0.002). FHL1 inhibited anchorage-dependent and -independent growth of human lung cancer cell lines. The inhibitory effects of FHL1 on lung cancer cell growth were associated with both the G1 and the G2/M cell cycle arrest concomitant with a marked inhibition of cyclin A, cyclin B1 and cyclin D as well as the induction of the cyclin dependent kinase inhibitors p21 (WAF1/CIP1) and p27 (Kip1). Direct intratumoral injection of an adenovirus expressing FHL1 dramatically suppressed the growth of A549 lung cancer cells in nude mice. Our data suggest that reduced expression of FHL1 may play an important role in the development and progression of lung cancer and that FHL1 may be a useful target for lung cancer gene therapy.

Four and a half LIM protein 1 (FHL1) has been linked to carcinogenesis. However, the role of FHL1 in lung cancer remains unclear and the detailed mechanism underlying its tumor suppressive role is poorly understood. The purpose of this study was to examine FHL1 expression in lung cancer patients and to investigate how it was associated with lung cancer cell growth. Immunoblotting and immunohistochemistry showed that FHL1 protein was downregulated in over 90% of 80 lung cancer patients. FHL1 expression was strongly correlated with tumor histological types (P<10(-4) ) and the differentiation of the tumor (P=0.002). FHL1 inhibited anchorage-dependent and -independent growth of human lung cancer cell lines. The inhibitory effects of FHL1 on lung cancer cell growth were associated with both the G1 and the G2/M cell cycle arrest concomitant with a marked inhibition of cyclin A, cyclin B1 and cyclin D as well as the induction of the cyclin dependent kinase inhibitors p21 (WAF1/CIP1) and p27 (Kip1). Direct intratumoral injection of an adenovirus expressing FHL1 dramatically suppressed the growth of A549 lung cancer cells in nude mice. Our data suggest that reduced expression of FHL1 may play an important role in the development and progression of lung cancer and that FHL1 may be a useful target for lung cancer gene therapy.

Four and a half LIM protein 1 (FHL1) has been linked to carcinogenesis. However, the role of FHL1 in lung cancer remains unclear and the detailed mechanism underlying its tumor suppressive role is poorly understood. The purpose of this study was to examine FHL1 expression in lung cancer patients and to investigate how it was associated with lung cancer cell growth. Immunoblotting and immunohistochemistry showed that FHL1 protein was downregulated in over 90% of 80 lung cancer patients. FHL1 expression was strongly correlated with tumor histological types (P<10(-4) ) and the differentiation of the tumor (P=0.002). FHL1 inhibited anchorage-dependent and -independent growth of human lung cancer cell lines. The inhibitory effects of FHL1 on lung cancer cell growth were associated with both the G1 and the G2/M cell cycle arrest concomitant with a marked inhibition of cyclin A, cyclin B1 and cyclin D as well as the induction of the cyclin dependent kinase inhibitors p21 (WAF1/CIP1) and p27 (Kip1). Direct intratumoral injection of an adenovirus expressing FHL1 dramatically suppressed the growth of A549 lung cancer cells in nude mice. Our data suggest that reduced expression of FHL1 may play an important role in the development and progression of lung cancer and that FHL1 may be a useful target for lung cancer gene therapy.

Morphogenesis of an organ. An organ is defined as a tissue or set of tissues that work together to perform a specific function or functions. Morphogenesis is the process in which anatomical structures are generated and organized. Organs are commonly observed as visibly distinct structures, but may also exist as loosely associated clusters of cells that work together to perform a specific function or functions.

Using a cDNA clone derived from a human muscle library we have identified a novel and highly conserved 2.3kb homologue which is highly expressed in skeletal muscle. The partial sequence contains at least three LIM domains and shows greatest homology with the group of LIM-proteins associated with the cytoskeleton and focal adhesion plaques which include zyxin and paxillin. This homologue is maximally expressed in differentiated ovine primary muscle cultures. It is also expressed in the ovine fetus from at least 50 days of gestation and is increasingly upregulated from 120 days of gestation to 8 weeks after birth after which it declines. This period corresponds to the period of greatest muscle fibre hypertrophy and suggests a role for this homologue in either the elaboration of muscle fibre matrix anchorage or the regulation of muscle fibre hypertrophy itself.

Any process that activates or increases the frequency, rate or extent of the directed movement of potassium ions (K+) into, out of or within a cell, or between cells, by means of some agent such as a transporter or pore.

AIMS: Protein-protein interactions are critical for the normal membrane trafficking, localization, and function of voltage-gated ion channels. In human heart, the Shaker-related voltage-gated K(+) channel KCNA5 alpha-subunit forms the major basis of an atrial-specific, ultra-rapid delayed rectifier K(+) current, I(Kur). We sought to identify proteins that interact with KCNA5 in human atrium and investigate their role in the I(Kur) complex. METHODS AND RESULTS: Using a glutathione-S-transferase (GST)-KCNA5 C-terminal fusion protein and mass spectrometry-based methods, the scaffolding protein four and a half LIM (for Lin-11, Isl-1, and Mec3) protein 1 (FHL1) was identified as a potential protein partner for KCNA5. Immunoprecipitation experiments confirmed a physical interaction of FHL1 with the K(+) channel complex in human atrium, as well as in Chinese hamster ovary (CHO) cells transfected with both KCNA5 and FHL1. In cotransfected cells, confocal microscopy demonstrated areas of colocalization after immunolabelling both proteins. To investigate the functional effects of this interaction, K(+) currents were recorded in CHO cells transfected with KCNA5 in the absence and presence of FHL1 coexpression. With coexpression of FHL1, K(+) current density was markedly increased, compared with cells expressing KCNA5 alone. This effect was associated with a shift in the voltage dependence of K(+) channel activation to more positive potentials, consistent with findings of I(Kur) in atrial myocytes. FHL1 also increased the extent and speed of K(+) current slow inactivation, with additional effects on the voltage dependence and recovery of this process. CONCLUSION: These results support a role of FHL1 as a key molecular component in the I(Kur) complex in human atrium, where it likely regulates functional expression of KCNA5.

Any process that modulates the rate, frequency or extent of membrane depolarization. Membrane depolarization is the process in which membrane potential changes in the depolarizing direction from the resting potential, usually from negative to positive.

AIMS: Protein-protein interactions are critical for the normal membrane trafficking, localization, and function of voltage-gated ion channels. In human heart, the Shaker-related voltage-gated K(+) channel KCNA5 alpha-subunit forms the major basis of an atrial-specific, ultra-rapid delayed rectifier K(+) current, I(Kur). We sought to identify proteins that interact with KCNA5 in human atrium and investigate their role in the I(Kur) complex. METHODS AND RESULTS: Using a glutathione-S-transferase (GST)-KCNA5 C-terminal fusion protein and mass spectrometry-based methods, the scaffolding protein four and a half LIM (for Lin-11, Isl-1, and Mec3) protein 1 (FHL1) was identified as a potential protein partner for KCNA5. Immunoprecipitation experiments confirmed a physical interaction of FHL1 with the K(+) channel complex in human atrium, as well as in Chinese hamster ovary (CHO) cells transfected with both KCNA5 and FHL1. In cotransfected cells, confocal microscopy demonstrated areas of colocalization after immunolabelling both proteins. To investigate the functional effects of this interaction, K(+) currents were recorded in CHO cells transfected with KCNA5 in the absence and presence of FHL1 coexpression. With coexpression of FHL1, K(+) current density was markedly increased, compared with cells expressing KCNA5 alone. This effect was associated with a shift in the voltage dependence of K(+) channel activation to more positive potentials, consistent with findings of I(Kur) in atrial myocytes. FHL1 also increased the extent and speed of K(+) current slow inactivation, with additional effects on the voltage dependence and recovery of this process. CONCLUSION: These results support a role of FHL1 as a key molecular component in the I(Kur) complex in human atrium, where it likely regulates functional expression of KCNA5.

AIMS: Protein-protein interactions are critical for the normal membrane trafficking, localization, and function of voltage-gated ion channels. In human heart, the Shaker-related voltage-gated K(+) channel KCNA5 alpha-subunit forms the major basis of an atrial-specific, ultra-rapid delayed rectifier K(+) current, I(Kur). We sought to identify proteins that interact with KCNA5 in human atrium and investigate their role in the I(Kur) complex. METHODS AND RESULTS: Using a glutathione-S-transferase (GST)-KCNA5 C-terminal fusion protein and mass spectrometry-based methods, the scaffolding protein four and a half LIM (for Lin-11, Isl-1, and Mec3) protein 1 (FHL1) was identified as a potential protein partner for KCNA5. Immunoprecipitation experiments confirmed a physical interaction of FHL1 with the K(+) channel complex in human atrium, as well as in Chinese hamster ovary (CHO) cells transfected with both KCNA5 and FHL1. In cotransfected cells, confocal microscopy demonstrated areas of colocalization after immunolabelling both proteins. To investigate the functional effects of this interaction, K(+) currents were recorded in CHO cells transfected with KCNA5 in the absence and presence of FHL1 coexpression. With coexpression of FHL1, K(+) current density was markedly increased, compared with cells expressing KCNA5 alone. This effect was associated with a shift in the voltage dependence of K(+) channel activation to more positive potentials, consistent with findings of I(Kur) in atrial myocytes. FHL1 also increased the extent and speed of K(+) current slow inactivation, with additional effects on the voltage dependence and recovery of this process. CONCLUSION: These results support a role of FHL1 as a key molecular component in the I(Kur) complex in human atrium, where it likely regulates functional expression of KCNA5.

Keywords

Protein involved in differentiation, the developmental process of a multicellular organism by which cells become specialized for particular functions. Differentiation requires selective expression of the genome; the fully differentiated state may be preceded by a stage in which the cell is already programmed for differentiation but is not yet expressing the characteristic phenotype determination. Also used for fungal conidiation proteins, and for some bacteria that present specialization of function in cell types, such as Caulobacter crescentus.

Protein which is part of a reference proteome. Reference proteomes are a subset of proteomes that have been selected either manually or algorithmically according to a number of criteria to provide a broad coverage of the tree of life and a representative cross-section of the taxonomic diversity found within UniProtKB, as well as the proteomes of well-studied model organisms and other species of interest for biomedical research.